Interpretive Summary: Phosphorus that is in soybeans is in a compound called phytic acid. Phytic acid can not be digested by animals. So most of the phosphorus in soybeans can not be used by animals for their nutrition and is excreted. This is a major source of phosphorus pollution in water systems, particularly in places with large concentrations of livestock that have soybean meal in their diets. Soybeans have been developed that are very low in phytic acid. This trait is being bred into soybean varieties. We have also discovered that there is natural variation for phytic acid content among soybean varieties that farmers grow. Those varieties that already have lower levels of phytic acid should be used in breeding programs aimed at developing phytic acid soybean varieties.

Technical Abstract:
Phytic acid in soybean meal is a major source of P in animal excreta, a serious environmental pollutant. A genetic mutant in which seed phytate is reduced by 70% has been developed. The objectives of this study were (1) to determine the natural variation in seed phytate P and phosphate P concentrations in soybean breeding lines and cultivars of maturity groups V and VI, (2) to assess the extent of genotype x environment interaction for both phosphate and PA-P in soybeans, and (3) to evaluate relations among PA-P, phosphate P, and seed protein concentrations. Three sets of cultivars and breeding lines were tested separately in three environments. Variation among lines in the three sets was highly significant, ranging from 3.86 to 5.08 g kg-1 phytate P and from 0.18 to 0.37 g kg-1 phosphate P. Genotype x environment interactions were significant for phosphate P concentration but not phytate concentration. Rank correlation coefficients between locations were large (0.65 to 0.88) suggesting that the genotype x environment interaction was due to differences in magnitude of phosphate P concentration in the various environments. Correlation coefficients between phytic acid and phosphate concentrations were 0.16, 0.47, and 0.63 in the three sets of materials. Variation in seed protein was highly significant in all three sets, but protein was not correlated with PA-P or phosphate P. Consideration of the phytic acid level of potential adapted parents may be useful in designing a breeding program for low phytic acid soybeans.